Polyurethanes have been known and used for many years, and the basic general chemistry for their preparation, the reaction of a polyol, a polyisocyanate and a chain extender, is fully documented.
A polyol frequently used for this purpose is PPG, which is well known to be degraded by exposure to oxygen, light and heat. It has been the general practice to guard against such degradation by blending with the PPG an external stabilizer such as a phenolic, an amine or a sulfur compound.
It has now been found, according to the invention, that the stabilization can be more effectively and efficiently achieved if the PPG is modified so that it contains in its chain 1-25%, by weight, preferably 3-15%, of moieties represented by the structure ##STR1## where R is hydrogen, an alkyl radical of 1-3 carbon atoms or phenyl, and the oxygen atom is linked to a hydrogen atom or a carbon atom.
Preferably, the modified PPG has an oxygen/sulfur atom ratio of 3/1 or greater, even more preferably 5-60/1.
It has been found, according to the invention, that the stabilization against degradation can also be achieved if the unmodified PPG to be used is physically blended with about 0.4-20%, by weight, of the modified PPG.
In addition, the method for preparing the modified PPG of the invention can be used to increase the molecular weight of the PPG by coupling polymer chain segments with HAS moieties.
It has also been found that PPG modified according to the invention shows significantly better resistance to acid-catalyzed depolymerization and to oxidative degradation at high temperatures than unmodified PPG.